More often than not, the September full moon is known by the nickname “harvest moon” because this is the prime harvest season for corn and other crops. But 2020 happens to be one of those off-years, where the moon calendar is a little out of whack.

So the full moon that will be glowing in the night sky this week will be known as the corn moon. The harvest moon nickname will be reserved for the next full moon, which appears on Oct. 1.

That will be the first of two full moons in October 2020 — so the second one will be considered a blue moon, making a rare appearance on Halloween.

When to see the September full moon

The moon will be officially full at 1:22 a.m. on Wednesday, Sept 2, and the best time to see it is when it begins to rise in the eastern sky.

It will look its biggest and brightest Tuesday night (99% full), Wednesday night (100% full) and Thursday night (98% full). If you are an early riser, don’t forget to look for the moon as it sets in the western sky.

For the moonrise and moonset times in your city, check TimeAndDate.com.

Why the harvest moon isn’t in September

The harvest moon nickname gets switched between September and October every few years, depending on which full moon appears closest to the date of the autumn equinox, the official start of the fall season. The equinox occurs when the sun rises directly over the equator, bringing an almost equal amount of daylight and darkness hours in the northern and southern hemispheres on that day.

In 2017, the autumn equinox occurred on Sept. 22, closer to the October full moon (Oct. 5) than the September full moon (Sept. 6). As a result, the October full moon of 2017 was called the harvest moon and the September full moon got the corn moon nickname.

The same thing is happening this year. The autumn equinox will also occur on Sept. 22, which will be closer fo the Oct. 1 full moon than the Sept. 2 full moon. So the early October full moon will get the harvest moon nickname, while the September full moon will be called the corn moon.

In 2018 and 2019, autumn started closer to the September full moon than the October full moon, so the September moon carried its traditional harvest moon nickname.

Other nicknames for the September full moon

As noted above, depending on how close to the autumn equinox the September moon turns full — it is sometimes known as the “corn moon” instead of the harvest moon. Some native American tribes call it the barley moon, “because it is the time to harvest and thresh the ripened barley,” the Old Farmer’s Almanac says.

A few other nicknames have been thrown into the mix for this month’s full moon.

Space.com says the September full moon was known as the “falling leaves moon” among the Ojibwe tribe in the Great Lakes region and also had two other nicknames: “The Cree of Ontario called the September full moon the rutting moon because it was when many animals started mating (notably, deer).

In the Pacific Northwest, the Haida called it the cedar bark moon, according to the ‘Tlingit Moon and Tide Teaching Resource’ published by the University of Alaska in Fairbanks.”